Highly integrated phase change memory device having micro-sized diodes and method for manufacturing the same

ABSTRACT

A highly integrated phase change memory device and a method for manufacturing the same is disclosed. The highly integrated phase change memory device includes a semiconductor substrate having a cell area and a peripheral area with impurity regions formed in the cell area and extending in parallel to each other in a first direction to form a striped pattern. A gate electrode is formed in the peripheral area and dummy gate electrodes are formed in the cell area and extending in a second direction perpendicular to the first direction of the impurity regions. An interlayer dielectric layer pattern exposes portions of the cell area and the peripheral area and a PN diode is formed in a space defined by a pair of dummy gate electrodes and a pair of interlayer dielectric layer patterns.

CROSS-REFERENCES TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. 119(a) to Koreanapplication number 10-2008-0049064, filed on May 27, 2008, in the KoreanPatent Office, which is incorporated by reference in its entirety as ifset forth in full.

BACKGROUND OF THE INVENTION

1. Technical Field

The embodiments described herein generally relate to a highly integratedphase change memory device and a method for manufacturing the same and,more particularly, to a highly integrated phase change memory devicehaving a micro-sized diode and a method for manufacturing the same.

2. Related Art

Generally, semiconductor memory devices are classified as volatilesemiconductor memory devices, such as a DRAM device or an SRAM device,which cannot retain data stored if power to the devices is shut off, andnon-volatile semiconductor memory devices, such as an EEPROM device,which can retain data stored even if power is shut off to the devices. Aflash memory device, which is classified as a non-volatile semiconductormemory device, is used primarily for electronic appliances such asdigital cameras, mobile phones, or MP3 players. However, newsemiconductor memory devices, such as an MRAM (magnetic RAM) device, anFRAM (ferroelectric RAM) device, and a PRAM (phase change RAM) devicehave been developed to replace flash memory devices since flash memorydevices requires a lot of time to record or read data.

Among those semiconductor memory devices mentioned above, the PRAMdevice stores data using a difference in resistance between an amorphousstate and a crystal state resulting from phase transition of achalcogenide compound. The PRAM device stores data as a “0” and “1”based on a reversible phase transition of a phase change material layerincluding the chalcogenide compound Ge—Sb—Te (GST) according to anamplitude and a length of a pulse applied thereto. More specifically, areset current is required for transitioning the phase change materiallayer into the amorphous state that has a higher resistance and a setcurrent is required for transitioning the phase change material layerinto the crystal state that has a lower resistance. The reset and setcurrents are transferred to the phase change material layer via aswitching device and a lower electrode contact that are positioned belowthe phase change material layer to activate the phase change.

Recently, as with other memory devices, the phase change memory devicehas become more highly integrated and a vertical diode having an areanarrower than that of a transistor is employed in the phase changememory device as a switching device.

Hereinafter, a method for manufacturing a vertical diode used in aconventional phase change memory device will be described with referenceto FIGS. 1 a to 1 c and 2 a to 2 c.

Referring to FIGS. 1 a and 2 a, a semiconductor substrate 10 having acell area A and a peripheral area B is prepared. An n-type impurityregion 15 is then formed in the cell area A. A gate material layer (notshown) is subsequently formed on the semiconductor substrate 10 havingthe impurity region 15. After formation of the gate material layer, thegate material layer is partially removed such that the gate materiallayer remains on the peripheral area B to form a gate electrode 20.

Referring to FIGS. 1 b and 2 b, an interlayer dielectric layer 25 isformed on the semiconductor substrate 10. A mask pattern 30 having aplurality of openings 32 is then formed on the interlayer dielectriclayer 25 to expose portions of the impurity region 15 formed in the cellarea A. The openings 32 determine the size of the diode to be formedlater. Accordingly, the openings 32 must be arranged having a smallpitch with small diameters so that a maximum number of openings 32 canbe formed in the cell area A.

As shown in FIGS. 1 c and 2 c, the interlayer dielectric layer 25 isetched using the mask pattern 30 as an etch mask to form contact holes Hfor exposing the impurity region 15. An SEG (selective epitaxial growth)layer 40 a is then grown to fill the contact holes H with the SEG layer40 a. The SEG layer 40 a serves as an n-type impurity layer since theSEG layer 40 a is grown from the n-type impurity region 15. Then, p-typeimpurities are implanted into the n-type SEG layer 40 a to form a p-typeimpurity region 40 b and thereby forming a PN diode 40.

As mentioned above, according to the conventional phase change memorydevice, the diode contact holes H must be arranged at a small pitch withsmall diameters to obtain a highly integrated phase change memorydevice. In the typical phase change memory device, a unit cell of thecell area A has an area of 1F2, which is smaller than an area (6F2) of aunit cell for a DRAM device. As a result, there has been suggested amethod of using a quadrupole type aperture (not shown) to form thecontact holes of the phase change memory device because the quadrupoletype aperture exhibits a higher optical efficiency than that of a dipoletype aperture used for forming storage node contact holes of the DRAMdevice. In other words, although the dipole type aperture isadvantageous in supplying light over a relatively large area, a smalleramount of light is supplied to a narrow area. For this reason, if thediode contact hole mask pattern 30 of the phase change memory device isformed using the dipole type aperture, the interlayer dielectric layer25 cannot be sufficiently exposed.

Meanwhile, a large amount of light can be supplied to the semiconductorsubstrate using the quadrupole type aperture. The amount of lightsupplied using the quadrupole type aperture is approximately two timesgreater than the amount of light supplied to the semiconductor substrateusing the dipole type aperture. Thus, a relatively greater amount oflight can be supplied to the narrow area if the quadrupole type apertureis adopted in the phase change memory device. As a result, the maskpattern 30 can sufficiently expose the interlayer dielectric layer 25.However, if an upper side of the mask pattern 30 is excessively exposedto the light, the mask pattern 30 may become deformed so that the shapeof the contact hole may become deformed (see, FIG. 1 c).

Additionally, as mentioned above, since the diode contact hole H isformed in a relatively narrow area (1F2), the contact hole may beaffected by the light used for forming an adjacent contact hole. Such aphenomenon is called a “side robe phenomenon”. When the side robephenomenon occurs, a dummy contact hole H1 may form in an undesiredregion. If a dummy contact hole H1 is formed as mentioned above, a diodeis formed in the dummy contact hole H1. This causes an electrical defectwith respect to a normal diode adjacent to the diode.

SUMMARY

A high integrated phase change memory device capable of preventing ashape of a diode from being deformed is described herein.

A method for manufacturing the high integrated phase change memorydevice is described herein.

According to one embodiment of the present invention, a highlyintegrated phase change memory device comprises a semiconductorsubstrate formed to have a plurality of conductive areas extending inparallel to each other in a first direction while forming stripepatterns, a plurality of first stripe patterns formed on thesemiconductor substrate and extending in parallel to each other in asecond direction perpendicularly to the first direction, a plurality ofsecond stripe patterns formed to expose the conductive areas whileforming a lattice structure together with the first stripe patterns, anda PN diode formed in a space defined by a pair of first stripe patternsand a pair of second stripe patterns to make contact with the conductiveareas.

According to another embodiment of the present invention, a highlyintegrated phase change memory device comprises a semiconductorsubstrate formed to have a cell area and a peripheral area, a pluralityof impurity regions formed on the cell area of the semiconductorsubstrate and extending in parallel to each other in a first directionwhile forming stripe patterns, a gate electrode formed on the peripheralarea of the semiconductor substrate, a plurality of dummy gateelectrodes formed on the cell area of the semiconductor substrate whilebeing aligned on a same plane with the gate electrode, and extending inparallel to each other in a second direction perpendicularly to thefirst direction, an interlayer dielectric layer pattern formed to exposethe cell area and the peripheral area while forming a lattice structuretogether with the dummy gate electrodes, and a PN diode formed in aspace defined by a pair of dummy gate electrodes and a pair ofinterlayer dielectric layer patterns to make contact with the cell areasand the peripheral areas.

According to still another embodiment of the present invention, a highlyintegrated phase change memory device is manufactured through thefollowing method. First, a semiconductor substrate formed to have a cellarea and a peripheral area is prepared. Then, a plurality of impurityregions extending in parallel to each other in a first direction whileforming stripe patterns are formed on the cell area of the semiconductorsubstrate. Next, a gate electrode is formed on the peripheral area ofthe semiconductor substrate and, at the same time, a plurality of dummygate electrodes are formed on the cell area of the semiconductorsubstrate. The dummy gate electrodes extend in parallel to each other ina second direction perpendicularly to the first direction. Then, aninterlayer dielectric layer pattern formed to form a lattice structuretogether with the dummy gate electrodes is formed such that theinterlayer dielectric layer pattern covers the peripheral area andexposes the impurity regions. After that, a PN diode is formed in theexposed impurity regions.

These and other features are described below in the section entitled“Detailed Description.”

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of thesubject matter of the present disclosure will be more clearly understoodfrom the following detailed description taken in conjunction with theaccompanying drawings, in which:

FIGS. 1 a to 1 c are plan views showing a method for manufacturing adiode of a conventional phase change memory device;

FIGS. 2 a to 2 c are sectional views showing a method for manufacturinga diode of a conventional phase change memory device, in which FIG. 2 ais a sectional view taken along line IIa-IIa′ of FIG. 1 a, FIG. 2 b is asectional view taken along line IIb-IIb′ of FIG. 1 b, and FIG. 2 c is asectional view taken along line IIc-IIc′ of FIG. 1 c;

FIGS. 3 a to 3 d are plan views shown for explaining methods formanufacturing a diode of a phase change memory device according to oneembodiment of the present invention;

FIGS. 4 a to 4 d are sectional views showing a method for manufacturinga diode of a phase change memory device according to one embodiment ofthe present invention, in which FIG. 4 a is a sectional view taken alongline IVa-IVa′ of FIG. 3 a, FIG. 4 b is a sectional view taken along lineIVb-IVb′ of FIG. 3 b, FIG. 4 c is a sectional view taken along lineIVc-IVc′ of FIG. 3 c, and FIG. 4 d is a sectional view taken along lineIVd-IVd′ of FIG. 3 d; and

FIG. 5 is a perspective view showing a diode of a phase change memorydevice according to one embodiment of the present invention.

DETAILED DESCRIPTION

Referring to FIGS. 3 a and 4 a, a semiconductor substrate 100 isprovided for fabrication of a phase change memory device. Thesemiconductor substrate 100 is divided into a cell area A and aperipheral area B. As is generally known in the art, many phase changepatterns (not shown) and many switching devices for selectivelyphase-changing the phase change patterns are formed in the cell area Aof the phase change memory device. Driving devices for the switchingdevices that are formed in the cell area A are provided in theperipheral area B. In a typical highly integrated phase change memorydevice, a diode having a small area can be used as the switching deviceand a MOS transistor can be used as the driving device.

N-type impurities are selectively implanted into the cell area A of thesemiconductor substrate 100 to form an impurity region 105. The n-typeimpurity region 105 serves as a word line in the phase change memorydevice. A plurality of n-type impurity regions 105 can be formed in thecell area A as shown in FIG. 3A. The n-type impurity regions 105 can bearranged in a striped pattern extending in a first direction and beingspaced parallel and apart from each other. The n-type impurities for then-type impurity region 105 include boron (B) ions, or arsenic (As) ions.

Next, a gate insulating layer 110 is formed on the entire surface of thesemiconductor substrate 100 having the cell region A and the peripheralregion B. A gate electrode layer 112 and a hard mask layer 113 are thensequentially formed on the gate insulating layer 110. For example, thegate electrode layer 112 includes a doped polysilicon layer, a silicidelayer, a metal layer, or a stacked structure thereof. The hard masklayer 113 may include a silicon nitride layer. A first mask pattern (notshown) is formed on the gate electrode layer 112 through aphotolithography process. The first mask pattern serves as a mask forforming a gate electrode in the peripheral area B. According to anembodiment of the present invention, the first mask pattern is used toform the gate electrode in the peripheral area B and to form a dummygate electrode in the cell area A. The hard mask layer 113 and the gateelectrode layer 112 are then etched using the first mask pattern as anetch mask to form a dummy gate electrode 115 a in the cell area A and agate electrode 115 b in the peripheral area B. The dummy gate electrode115 a and the gate electrode 115 b can be further formed by forming aninsulation spacer 114 at sidewalls of the remaining hard mask layer 113and the gate electrode layer 112.

Accordingly, a plurality of dummy gate electrodes 115 a can be formedparallel to each other in the cell area A. The dummy gate electrodes 115a are arranged in a striped pattern extending in a second direction thatis perpendicular to the impurity regions 105 that extend in the firstdirection. An interval between the dummy gate electrodes 115 a can bedetermined by taking the number of phase change patterns to beintegrated on the cell area A into consideration. In addition, anadditional lithography process for forming the dummy gate electrodes 115a is not necessary since the dummy gate electrodes 115 a are formedtogether with the gate electrodes 115 b using one mask pattern. Thefirst mask pattern is then removed through a removal process generallyknown in the art.

As shown in FIGS. 3 b and 4 b, an interlayer dielectric layer 120 isformed on the semiconductor substrate 100 including the gate electrode115 b and the dummy gate electrodes 115 a. The interlayer dielectriclayer 120 may include silicon oxide components and formed as a singlelayer or a multi-layer. The interlayer dielectric layer 120 has athickness sufficient for filling a gap left between the dummy gateelectrodes 115 a. An upper surface of the interlayer dielectric layer120 can be subsequently planarized through a polishing process.

A second mask pattern 125 is formed on the interlayer dielectric layer120 through a photolithography process. The second mask pattern 125according to an embodiment of the present invention, serves as a mask todefine contact holes. Accordingly, the second mask pattern 125 exposes apredetermined portion of the interlayer dielectric layer 120corresponding to the impurity region 105 while blocking the peripheralarea B. Thus, the second mask pattern 125 has slits 127 for exposing thepredetermined portion of the impurity region 105 as shown in FIG. 3B. InFIG. 4 b, reference numeral 125 a refers to the second mask patternaligned on the cell area A and reference numeral 125 b refers to thesecond mask pattern aligned on the peripheral area B.

Referring to FIGS. 3 c and 4 c, the exposed interlayer dielectric layer120 is etched using the second mask 125 (see, FIGS. 3 b and 4 b) as anetch mask to form an interlayer dielectric layer pattern 120 a. Thesecond mask pattern 125 is then removed through a removal processgenerally known in the art. In FIGS. 3 c and 3 d, the dashed linesindicate those areas and structures that are formed beneath theinterlayer dielectric layer pattern 120 a and thus hidden from view.That is, the interlayer dielectric layer pattern 120 a is formed overthe entire structure of FIGS. 3 c and 3 d except for the regionsdesignated by solid lines. The interlayer dielectric layer pattern 120 ablocks the peripheral area B and the exposed portions of the impurityregion 105 through the interlayer dielectric layer pattern 120 a forms alattice structure in conjunction with the dummy gate electrodes 115 a inthe cell area A. That is, the interlayer dielectric layer pattern 120 ahas a striped structure extending perpendicularly to a direction offormation for the dummy gate electrodes 115 a. Thus, predeterminedportions of the impurity region 105 are exposed at a predeterminedinterval according to the dummy gate electrodes 115 a and the interlayerdielectric layer pattern 120 a formed in the cell area A, which arealigned in the lattice structure, so that contact holes 130 are formedin a self-alignment scheme.

Referring to FIGS. 3 d and 4 d, an n-type SEG layer 135 a is grown fromthe impurity region 105 through a selective epitaxial growth scheme. Then-type SEG layer 135 a may be formed to have a height substantially thesame as a height of the interlayer dielectric layer pattern 120 a.N-type impurities can also be additionally doped when forming the n-typeSEG layer 135 a. After initial formation of the n-type SEG layer 135 a,p-type impurities are doped into the n-type SEG layer 135 a to form ap-type impurity region 135 b, thereby forming a PN diode 135.

Although not shown in the drawings, a bottom electrode, a phase changepattern, and a top electrode are formed on the PN diode 135.

FIG. 5 is a perspective view showing the diode of the phase changememory device according to an embodiment of the present invention.

Referring to FIG. 5, the diodes 135 are formed in spaces (holes) definedby a pair of dummy gate electrodes 115 a extending in the firstdirection and a pair of interlayer dielectric layer patterns 120 aextending in the second direction. Thus, the diodes 135 are insulatedfrom each other in the first direction by the interlayer dielectriclayer patterns 120 a and are insulated from each other in the seconddirection by the dummy gate electrodes 115 a. Accordingly, the diodes135 can be sufficiently insulated from each other since the dummy gateelectrodes 115 a are covered with the hard mask layer and the spacer ina floating state.

According to one embodiment of the present invention, the dummy gateelectrode 115 a extends perpendicular to the impurity region 105, whichserves as the word line, and is formed in the cell area A when the gateelectrode is formed in the peripheral area B. Diode contact holes forforming the diodes are then formed in a self-alignment scheme instead ofdirectly forming the contact holes using the interlayer dielectric layerpattern 120 a extending perpendicularly to the dummy gate electrode 115a to expose the impurity region 105.

Therefore, the diode contact holes can be formed through the selfalignment scheme so that an influence upon the aperture can be reducedby forming striped patterns without the need for using a mask patternhaving openings aligned at a small pitch with small diameters. As aresult, deformation of the contact hole shape caused by defectiveexposure process can be prevented.

According to one embodiment of the present invention, the dummy gateelectrode is formed in the cell area while the gate electrode is formedin the peripheral area. The diode contact holes are then formed throughthe self alignment scheme by forming the interlayer dielectric layerpatterns perpendicularly to the dummy gate electrodes to expose theimpurity region without directly forming the contact holes for thediodes.

Influence upon the aperture can be reduced since the diode contact holescan be formed through the self alignment scheme by forming the stripedpatterns without the need for using a mask pattern having openingsaligned at a small pitch with small diameters. Thus, deformation of thecontact hole shape caused by the defective exposure process can beprevented. Accordingly, various types of apertures can be used.

While certain embodiments have been described above, it will beunderstood that the embodiments described are by way of example only.Accordingly, the systems and methods described herein should not belimited based on the described embodiments. Rather, the systems andmethods described herein should only be limited in light of the claimsthat follow when taken in conjunction with the above description andaccompanying drawings.

What is claimed is:
 1. A high integrated phase change memory device,comprising: a semiconductor substrate formed to have a plurality ofconductive areas extending parallel to each other in a first directionthereby forming a striped pattern; a plurality of first stripe patternsformed on the plurality of the conductive, areas of the semiconductorsubstrate and extending parallel to each other in a second directionthat is perpendicular to the first direction; a plurality of secondstripe patterns formed on the plurality of the first stripe patterns toperpendicularly arrange to the plurality of the first stripe patternssuch that portions of the conductive areas are exposed and therebyforming a plurality of diode spaces which are surrounded by the firststripe patterns and the second stripe patterns; and a plurality of PNdiodes formed to contact the exposed portion of the conductive areas inthe diode spaces.
 2. The high integrated phase change memory device ofclaim 1, wherein the conductive areas include n-type impurity regions.3. The high integrated phase change memory device of claim 1, wherein aPN diode among the plurality of PN diodes is electrically isolated bythe first and second stripe patterns.
 4. The high integrated phasechange memory device of claim 1, wherein the first stripe patterns areelectrically floated.
 5. The high integrated phase change memory deviceof claim 4, wherein the first stripe patterns include dummy gates. 6.The high integrated phase change memory device of claim 5, wherein thesecond stripe patterns include insulating layer patterns.
 7. The highintegrated phase change memory device of claim 6, wherein the secondstripe patterns are formed to a height taller than a height of the firststripe patterns.
 8. The high integrated phase change memory device ofclaim 7, wherein a PN diode among the plurality of PN diodes has aheight identical to the height of the second stripe patterns.
 9. A highintegrated phase change memory device, comprising: a semiconductorsubstrate having a cell area and a peripheral area; a plurality ofimpurity regions formed in the cell area of the semiconductor substrateand extending parallel to each other in a first direction therebyforming a striped pattern; a gate electrode formed on the peripheralarea of the semiconductor substrate; a plurality of dummy gateelectrodes formed in the cell area of the semiconductor substrate andbeing aligned coplanar to the gate electrode, and extending in parallelto each other in a second direction that is perpendicular to the firstdirection; an interlayer dielectric layer pattern formed to expose thecell area and the peripheral area and forming a plurality of diodespaces; and a plurality of PN diodes formed to contact the exposed cellarea in the diode spaces defined by a pair of dummy gate electrodes anda pair of interlayer dielectric layer patterns.
 10. The high integratedphase change memory device of claim 9, wherein the dummy gate electrodesare electrically floated.
 11. The high integrated phase change memorydevice of claim 9, wherein the interlayer dielectric layer pattern isformed to a height taller than a height of the dummy gate electrodes anda PN diode among the plurality of PN diodes has a height identical tothe height of the interlayer dielectric layer pattern.